Kriss USA. But I don't know if they will sell them. I got the lower housing as an upgrade/replacement when I sent my real steel in for warranty work. I asked them to return any parts they replaced. Since I sent the real steel in without the stock, they had to charge me for a replacement stock in order to ship it back directly to me. They were worried about the legality of it due to NY stupid laws.

The upper receiver was bought cause I have a hook up. But it sounds like they don't normally sell the polymer housings.